Three brothers -- ages 8, 10 and 16 -- were floating down Salmon Creek near Salmon Creek Regional Park Wednesday afternoon when their kayak overturned, Clark County Fire District 6 Chief Jerry Green told NBC News. The park is in Washington state just north of Portland, Ore.

Ten prison inmates from the Larch Corrections Center near Yacolt, Wash., were doing park maintenance when they heard screams for help and responded quickly, fire officials told The Columbian newspaper in Vancouver, Wash.

Inmate Nelson Pettis, 37, jumped into the strong current, floating downstream until he could grab the two younger boys and help them to a pile of floating debris, according to the newspaper.

"I don't think I was thinking at all," Pettis told The Columbian. "I was just really concentrating on getting them to safety."

Inmate Larry Bohn, 29, helped Pettis with the rescue: "They (the boys) were saying thank you repeatedly. They just seemed really scared," he told the newspaper.

The 16-year-old boy was able to swim to shore, Green told NBC News.

Inmate Jon Fowler, 28, waited for the rescue team to arrive and helped them inflate their rescue boat, The Columbian reported. Members of the Vancouver, Wash., Fire Department and Clark County Fire District 6 were part of the rescue team.

The water was "very cold" and estimated to be moving at 25 mph, Green said. The brothers were treated for mild hypothermia, but otherwise there were no other injuries, he said. Two of the inmates were also treated for hypothermia, Portland, Ore., NBC affiliate KGW reported.

Bohn and Pettis reportedly had taken off their shirts, wrapping them around the kids to keep them warm, The Columbian reported.

The boys' names were not released.

Green said he was "extremely impressed" with the prisoners' efforts and the fact that they jeopardized their safety.

"(They) stepped up and did what was the right thing to do," Green said.

"I don't think we're heroes by any means," inmate Fowler told The Columbian. "I think we just did what any good person would do."

Nancy Simmons, a spokesperson for the Larch Corrections Center, told NBC News the brothers want to thank the inmates who helped and a meeting with their family is in the works.

This correction facility houses inmates who are not there for violent crimes and who generally have four years or less left on their sentences, Simmons said.